As mentioned above, the invention pertains to grass catchers for lawn mowers. Although aspects of the invention could conceivably be used on many types of grass catchers, even on grass catchers for walk-behind reel mowers, the preferred catcher according to the invention is used in conjunction with riding rotary lawn mowers or lawn tractors. The following discussion will focus almost exclusively on lawn tractors, but those skilled in the art will recognize that the invention could be applied to other types of mowers as well.
A lawn tractor includes a traction vehicle which carries a rotary grass cutting unit. The cutting unit includes a deck beneath which is a rotatable blade powered by the traction vehicle's prime mower. Attached to the mower deck is a discharge elbow which guides the grass clippings, leaves, debris, etc., into an upwardly-inclined discharge tube which terminates at its upper end in a closed hood. The hood typically covers one or more upwardly-opening flexible grass bags and serves to evenly distribute the grass, etc., between the bags. The flexible bags are attached to and hang from square or rectangular frames which are cantilevered from the back end of the lawn tractor. Although aspects of the invention could be applied to other types of grass catchers, for the sake of brevity the following discussion will focus on the "flexible bag" catcher described immediately above.
Although prior "flexible bag" grass catchers are generally adequate for their intended purposes, they are hindered by at least three problems which have heretofore been inadequately addressed. One longstanding problem with such catchers is that it has always been very difficult to conveniently determine, during operation of the lawn tractor, when the bags are full and in need of emptying. Secondly, as the bags fill a gap tends to develop between the tops of the bags and the bottom of the hood, leading to grass "leakage" through the gap. Finally, the hoods, which are oftentimes mounted using an overcenter spring-loaded hinge scheme, are susceptible to popping open when the mower is driven over rough ground.
With regard to the difficulty of determining when the catcher is full, several techniques have been tried. probably the most common type of "fill detector" is a transparent window in the hood or in the discharge tube. With a window in the hood, at least theoretically the operator can occasionally look directly into the grass bags to determine their status. With a window in the discharge tube the operator can theoretically directly observe whether the grass clippings are flowing upwardly and rearwardly into the grass catcher at the normal rate. Windows of this type possess several inadequacies, however. For one thing, clipping monitoring windows tend to reflect light. Depending on the angle of the sun relative to the window, the glare can make it difficult for the operator to observe what is happening inside the hood or discharge tube. Even more of a problem is the fact that clipping monitoring windows tend to become stained and dirty after a short period of time thus making them more opaque than transparent. Finally, the operator must actually divert his or her attention from operating the mower to peer in the clipping monitoring window.
The second common type of "fill detector" is based on an air flow or pressure phenomenon. Reference is made to U.S. Pat. No. 3,971,198, for example, which shows an air flow detector built into the hood of a walk-behind rotary mower grass catcher. When the detector is spinning the air flow is adequate and the bags are capable of receiving additional grass, leaves, etc. However, when the detector stops spinning, this indicates to the operator that it is time to empty or dispose of the grass bags. A similar system involves, in effect, monitoring the air pressure within the discharge tube, hood, etc. Reference is made to U.S. Pat. No. 4,589,249. When the back pressure becomes excessively high, a horn or beeper can sound to signal the operator that the bags need emptying or changing. A visual indicator such as a red light could also be used to signal this state of affairs. As in the case of the window-type fill detectors discussed above, the operator usually must at least for a short time divert his or her attention from operating the mower to visually scan the air flow or air pressure type fill detector. An audible signal is possible, as disclosed in U.S. Pat. No. 4,589,249, but such a signal would have to be extremely loud to be heard over the noise of a lawn tractor, and would be unnecessarily expensive as well.
As noted above, another problem with pre-existing grass catchers is grass leakage between the hood and the grass bags. The cause of the problem is clear: the grass catcher hood and the bag frames are usually independently connected to the traction vehicle, so that when the bags are even partially filled with damp, lush grass, they naturally tend to sag downwardly. What's worse is that the bags usually fill at different rates and sag at different rates, so that even if the hood is spring loaded to keep it in contact with the bag frames, the hood would only engage the lightest bag, i.e, the one which has sagged the least. This results in a gap between the bag (or bag frame) which has sagged the most and the bottom edge of the hood. Such a gap can obviously allow grass clippings to escape.
As noted above, some hoods are spring-loaded in an attempt to minimize the gap between the hood and the grass bags. Such a technique can actually exacerbate the hood popping open problem also discussed above. The typical spring-loading mechanism applies a downward force to the hood when the hood is in its "full down" position but once the hood is separated from the bag frames by a short distance the spring goes overcenter and actually assists in lifting the hood off of the bag frames. Applicant has observed that hoods can pop open as lawn tractors are driven over fairly rough terrain, presumably because the hood springs have gone overcenter.
U.S. Pat. No. 4,637,202, assigned to The Toro Company, discloses one technique for addressing the "gap" and hood popping problems outlined above. Each grass bag is suspended from a bag frame which includes a pair of substantially parallel rearwardly-pointing hand grip elements. The hand grip elements can be squeezed toward one another and fit into a mating bracket attached to the catcher hood. While this securely mates the bag frames to the hood, the system is somewhat costly and also the hood cannot simply be slammed shut; the operator must instead take the time to manipulate the hand grip elements so as to secure the bag frames to the hood.
The present invention addresses the problems discussed above with prior art grass catchers, i.e., detecting full bags, stopping "hood popping," and preventing grass leakage between the hood and the grass bags. The invention is summarized below and discussed in some detail with reference to the appended Drawing.